9Y.  IT; 


Circular  No.  1 17. 


Issued  February  25,  L910 


United  States  Department  of  Agriculture, 

BUREAU   OF   ENTOMOLOGY. 
L.  O.  HOWARD.  Entomologis 


THE  WESTERN  <: 

i  ( \  jit,  a  s  occidt  uli 

By    I'. 
/;;  Cha  '  I      cut  unit 

(■KO.     I.     Kl 

Sin  citil    l"n  ill     \in  nl 
IXTRODVCTIOX. 

■;i — tem    saw  fly   [Ve\ 


u, 


The   western    gra — tem    sawfly  {C'eplu 
Marlatt),  which  has  caused  much  alarm  ami  irot-a  li 
wheal  growers  of  S'orth  Dakota  during  the  season  of  1909,  is  not  by 
any  means  a  ne'w   insect,  although  this  is  it-  first  appearance  in  the 


Fn      I.      Western   Brass-stem   snwflj     [Cephun  occidentalism:   u.   Larva;    6,   female   sawfly; 
isa  stem  showing  work      c,  Rnlarged  ;  </.  h.  more  enlarjied.      (From  Marlatt.  I 

United  States  a-  a  serious  pest.     It  was  firsl  observed  in  lx'-'<>  and  has 
since  been   reported  at   intervals  as   feeding  upon  grasses  and  occa 
sionally  upon  wheal  in  Canada  and  the  United  States.     For  the  pur 
pose  of  affording   farmers  all  available  information   relative  to  the 
2204H     \...   1  i  t"    It) 


2 

pest  this  circular  has  been  prepared.  The  account  of  the  habits  and 
seasonal  history  of  the  insect,  list  of  food  plants,  and  description  of 
both  larva  and  adult  represent  the  work  of  the  many  observers  men- 
tioned in  the  paragraph  on  history  and  distribution,  as  do  also  the  clos- 
ing statements  as  to  natural  cheek-  upon  it-  increase,  and  preventive 
treatment. 

HISTORY    AND  DISTRIBUTION. 

The  first  observation  on  this  insect  was  made  by  Mr.  Albert 
Koebele."  an  agent  of  this  office,  who  found  the  larvae  burrowing  in 
grass  stems  in  California  in  1890,  and  who  reared  the  adult-.  From 
these  and  others  which  had  been  collected  in  Montana  and  Nevada  the 
species  was  described  by  Riley  and  Marlatt,  who  said:  "The  eco- 
nomic importance  of  this  species  arises  from  the  fact  that  it  may  be 
expected  at  any  time  to  abandon  its  natural  food  plant  in  favor  of 
the  small  grains,  on  winch  it  can  doubtless  successfully  develop. 
Such  changes  in  the  food  habits  of  our  native  insects  are  constantly 
occurring  to  the  great  detriment  of  our  agriculture,  as  i-  illustrated 
by  the  attack  of  the  Nematus  and  Dolerus  species  on  wheat,  these 
insects  normally  affecting  wild  grasses." 

The  fulfillment  of  this  prophetic  suggestion  was  not  long  delayed. 
In  1896  the  late  Dr.  James  Fletcher.''  entomologist  to  the  Dominion 
of  Canada,  reported  that  he  had  found  the  adults,  which  he  be- 
lieved were  those  of  Cephus  pygmceus  L.,  the  European  species,  at 
Indian  Head.  Northwest  Territories  [Saskatchewan  | .  and  that  Mr. 
John  Wenman,  of  Souris,  Manitoba,  had  sent  in  wheat  straw-  con 
taining  larvae.  Mr.  Wenman  wrote  that  the  damage  resulting  from 
this  attack  was  not  appreciable.  In  1902  Doctor  Fletcher'  found 
the  larva'  numerous  in  grasses  in  the  Northwest.  In  L905,  1906,  and 
1907  the  junior  author  observed  the  work  of  the  larvae  in  grasses 
throughout  the  northwestern  United  States,  and  in  1906  found  them 
damaging  wheat  at  Kulm.  X.  Dak.  In  his  report  for  the  year  l'.MIs 
Doctor  Fletcher  again  referred  to  tins  insect,  stating  that  in  the  pre- 
vious autumn  it  had  appeared  in  central  Manitoba  and  the  south 
eastern  part  of  Saskatchewan  in  much  more  serious  number-  than  at 
any  previous  time.  "  The  broken  straws  which  resulted  from  its  attacks 
were  seen  in  many  fields  and  occasioned  some  alarm."  Mr.  Norman 
( 'riddle ''--a  farmer  and  careful  observer  of  insects,  of  Aweme, 
Manitoba,  and  the  inventor  of  the  grasshopper  poison  which  bears 
his  name — recognized  the  insect  a-  Cephus  occidentalism  and  wrote 
Doctor  Fletcher  at  the  end  of  the  season  that  the  species  had  increased 


Insert    Life.   Vol.   III.  |>.  71.    1S90. 
''Ann.  Rep.  Exp.  Farms  Canada  f.  1896,  pp.  229  230.  1897. 
<•■  Letter. 

''Ann.  Rep.  Exp.  Farms  Canada  f.  1907  S,  pp.  mi    192,  1909. 
ICir.  1171 


3 

considerably  during  the  last  year  or  two  and  had  turned  its  attention 
in  wheal  and  rye.  In  1908  the  authors  found  it  in  grasses  in  the 
Willamette  Vallej  in  Oregon.  In  1909  Prof.  II.  B.  Penhallow,  of 
New  York  City,  writing  from  Sherwood.  X.  Dak.,  stated  that  it 
was  damaging  from  '>  to  25  per  cent  of  the  wheat  in  man)  fields 
in  i he  Souris  Valley,  and  Mi'.  R.  VV.  Sharpe,  of  Fargo,  X.  Dak.. 
reported  similar  depredations  in  the  Red  River  Valley.  Larva'  or 
adults  have  been  found  in  Manitoba,  the  Dakota-.  Nebraska,  Kansas 
(probably),  Saskatchewan,  Montana,  Wyoming,  Colorado,  Oregon. 
\c\  ada.  and  Call  fornia. 

II  VBITS    VXD   SEASOM  \l.    HISTORY. 

In  Manitoba,  according  in  Mr.  Criddle,"  the  eggs  are  laid  singlj 
by  the  female  sawfly  i  fig.  1.  b)  upon  a  stem  of  grass  or  wheat,  not 
far  from  the  head,  between  June  20  and  the  second  week  id'  July. 
••The  larva'  (fig.  1.  a)  soon  hatch  and  begin  to  eat  down  inside  the 
stem,  usually  reaching  the  ground  toward  the  end  of  August,  at 
which  time  they  mature."  They  then  cut  a  horizontal  ring  on  the 
interior  of  the  stem  near  (he  surface  of  the  ground  so  a-  nearly  to 
sever  it.  after  which  the\  close  the  cavity  below  smoothly  with  a  plug 
id'  castings  and  -pin  a  thin,  silken,  cylindrical  cocoon  below  the  plug 
(fig.  1.  i  i.  The  -tem  usually  breaks  oil'  neatly  at  the  engraved  ring 
during  the  autumn,  hut  may  remain  in  position  until  winter  and 
possibly  longer.  "In  these  retreats,"  to  quote  again  from  Mr.  Crid 
die.  "the  larvae  pass  the  winter  and  remain  in  an  active  condition 
unchanged  until  May  of  the  following  year,  when  they  turn  to  pupa?. 
and  emerge  a-  perfect  sawflies  toward  tin'  end  id'  dune,  the  date  vary 
ing  somewhat  with  the  season."  The  adults  were  taken  by  Doctor 
Fletcher,'  duly  5,  on  the  flowers  of  tumbling  mustard. 

The  injured  stem  appears  discolored  between  the  first  and  third 
joint-  and  the  larva  may  he  seen  through  the  translucent  wall  of  the 
?tem  when'  ii  is  eaten  thinnest.  In  the  case  of  wheal,  the  stalk  often 
bends  at  this  point,  an  inch  or  two  below  a  joint  rather  than  above 
a-  in  He— ian  fly  injury,  and  the  head  fall-  to  the  ground  shortly 
before  harvest.     Dr.  d.  II.  Comstock'   found  that  the  European  corn 

-awtlv.  an  allied  species,  did   not    affect   I  he  size  of  the  head  or  of  the 

kernels,  but  it  is  well  known  that  grasses  have  the  heads  blighted  by 
our  species,  and  Professor  I'enhallovv  writes  that  the  head-  id'  wheat 
are  shrunken  Owing  In  the  diver-ion  id'  sap  at  this  critical  time.  If 
this  l»e  generally  true,  the  damage  to  the  crop  i-  much  greater  than 
ha-  been  estimated  from  the  number  of  fallen  head-.     Mi-,  ('riddle" 


"Ann.  Rep.  Exp.  Farms  Ca  inula  f.  1907  8,  pp.  191    192.  1909. 
i.  Rep.  Exp.  Farms  Canada  t'.  1896,  pp.  229  230,  1897 
i:nl.  ll.  Cornell  Univ.  Agr.  Exp.  Sta.,  N'ovember,  IS89. 

I  171 


states  that  in  a  field  of  wheat  at  Awenie,  .Manitoba.  75  per  cent  of  the 
infested  stems  collapsed  before  harvest,  but  we  observed  a  field  at 
Kulm,  X.  Dak.,  to  have  only  6  per  cent  of  the  injured  straws  broken. 
The  native  grasses  do  not  collapse  when  attacked  by  this  insect  and  it 
is  possible  that  some  stiff-stemmed  wheats  may  stand  up  better  than 
other  varieties.  This  is  an  advantage  to  the  fanner  in  preventing 
total  loss  of  the  affected  heads,  but  a  disadvantage  if  it  prevents 
him  from  detecting  the  cause  and  extent  of  a  serious  shrinkage  of 
the  kernels. 

The  damage  has  been  confined  heretofore  to  the  edges  of  fields 
bordered  by  grass  lands  or  roadsides.  Mr.  Criddle"  states  that  50 
per  cent  of  the  stand  is  infested  for  a  distance  of  100  feet  into  the 
fields,  and  that  the  damage  is  apparent  to  a  lesser  extent  throughout 
the  crop.  Pie  also  states  that  the  insect  seeks  wheat  only  when  it 
fails  to  find  enough  flowering  stem-  of  grasses  in  which  to  deposit 
its  eggs.  Recent  reports  from  North  Dakota  indicate  that  the  injury 
may  be  more  general  than  heretofore  and  suggest  that  the  insect  has 
probably  adapted  its  habits  to  conform  to  the  farm  methods  of  thai 
region  so  that  it  no  longer  depends  upon  native  grasses  1  nit  breed- 
throughout  the  fields,  at  once  distributing  the  damage  more  evenh 
and  increasing  its  capacity  for  harm.  A  pest  which  can  take  advan- 
tage of  wild  food  plants  and  yet  be  independent  of  them  is  far  more 
dangerous  than  one  which  can  feed  only  upon  wheat  or  one  which 
requires  both  wheat  and  a  native  grass. 

FOOD    PLANTS. 

This  sawlly  is  a  native  insect  which  has  learned  to  attack  wheat  and. 
according  to  Mr.  Criddle,  rye  also,  since  these  have  taken  the  place 
of  its  native  food  plants — quack  grass  and  wheat  grass  (  Agropyron  i. 
brome  grass  (Bromus),  rye  grass  (Elymus),  and  timothy  (Phleum). 
It  was  especially  abundant  in  Agropyron  along  railroad  embank 
ments  in  North  Dakota  in  1905  and  1906,  so  that  in  many  clumps 
of  this  grass  onedialf  of  the  heads  were  prematurely  whitened. 

DESCRIPTION. 

The  larva  (fig.  1.  a)  is  about  three-fifths  of  an  inch  long  and  one- 
eighth  as  wide,  slightly  Larger  near  the  head,  and  tapering  toward 
the  tail,  which  ends  in  a  small,  blunt,  upturned,  brown  tubercle.  The 
body  is  yellowish  white:  the  head,  a  spot  on  the  back  of  the  neck, 
rings  on  the  palpi,  the  tips  of  the  paired  cerci.  and  the  setae  on  the 
last  segment,  are  pale  yellow:  the  margin  of  the  cheeks  and  of  the 
antenna!  segments,  a  faint  streak  on  each  cheek  through  the  eye.  the 
mandibles,  the  stigmata,  and  the  median  anal  tubercle,  are  mahogany 

"  Loc.  cit. 
[Clr.  117] 


.) 

brown;  the  mandibles  shade  to  black  ;il   the  t  i f » —  and  ;ii   the  hii 
the  eyes  are  black. 

The  adult  (fig.  1.  I>)  is  a  black,  shining,  four-winged  saw  fly,  about 
one-third  of  an  inch  long,  spotted  and  banded  with  yellow.  The 
original  description"  is  as  follows: 

The  ;uliili    insect  agrees  almost   exactly  with  Ci  pint*  iii/ymtrux  in  colont 
coming  much  '-loser  to  it  in  tliis  respect  than  to  any  other  American  species,  but 
is  in  every  way  more  slender  and  graceful  and  would  never  be  mistaken  for  the 
European  species.    The  head  is  narrower  in  proportion  to  the  body  aud  is  more 
globular  when  viewed  from  the  side.     Viewed  frou  uarrows  more  pos 

teriorlj    from   the  eyes  than  iii/iiiikiiis.     *     *     * 

The  species  may  be  characterized  as  follows: 

2  Black;  basal  joints  of  the  maxillary  palpi,  large  spol  on  mandibles,  two 
spots  beneath  anterior  wings,  membranous  regions  of  thorax,  small  spot  on 
lower  posterior  edge  of  dorsum  of  first  segment,  larger  one  on  second  segment, 
band,  dentate  on  basal  margin,  on  apical  half  of  dorsum  of  third,  fifth,  and 
sixth  segments,  and  more  or  less  of  the  lower  and  apical  margin  of  the  re 
maining  segments,  lemon  yellow. 

Legs  black,  slender:  spot  on  posterior  coxa-  above,  upper  side  and  tip  of 
femora,  yellow;  tibiae  and  tarsi  reddish  yellow  except  tips  of  posterior  tibia1 
and  their  tarsi,  which  are  brownish;  last  joint  and  .laws  of  middle  and  an- 
terior tarsi  also  brownish. 

Antenna'  20  i'|  jointed,  longer  than  head  and  thorax,  slender  to  joint  T. 
beyond  which  the  articles  are  shorter  and  thickened 

Wings  slightly  smoky:  veins  brown  except  costal  and  margin  of  stigma. 
which  are  yellowish:  a  small  infuscated  spot  at  base  of  discoidal  vein:  second 
recurrent  vein  joins  the  third  submarginal  cell  near  the  base  of  the  cell;  cross 
veins  of  lanceolate  cell  slightly  curved  and  oblique. 

Abdomen  not  much  longer  than  bead  and  thorax,  strongly  compressed 
laterally. 

Lengt  h.   '.»    I  1    nun. 

Exp.  al.,    16   19  mm. 

$  smaller  and  more  slender  than  the  9:   abdomen  less  c pressed;   antenna' 

18  21  jointed.  Coloration  as  in  ?  except  a  large  spot  on  the  clypens.  one  jnsl 
below  the  eyes  in  front,  the  entire  pectal  region  of  the  thorax,  and  the  posterior 
margin  of  the  third,  fifth,  and  remaining  ventral  segments,  which  are  lemon 
\  ellow. 

The  miller  side  of  the  coxa?,  trochanters,  and  femora,  including  the  apex  of 
the  latter  above,  are  lemon  yellow;  the  tibia-  and  tarsi  are  as  in  the  case  of 
the    $. 

In  some  specimens  the  femora  are  entirely  yellow  or  with  a  narrow  black 
line  on  the  anterior  pair  above,  and  the  yellow  band  on  the  third  ventral  seg- 
ment is  occasionally  obsolete. 

Length,  s  0  nun. 

Exp.  al.,  15   IT  nmi. 

Habitat:  Santa  Clara  County  and  Santa  i 'in/  Mountains,  California,  Sevada, 
and    Montana. 

Described  from  2-t  females  and  II  males,  of  which  'S*  specimens  from  Cali- 
fornia were  bred  bj  Mr.  Koebele,  and  1.".  from  Nevada  and  Montana  were 
collected. 


Insect   Life,  Vol.  IV.  pp.  177    17s.   I  Sill. 
[Cir.  1 171 


NATURAL    CHECKS. 

Mr.  ('riddle  found  thai  many  of  the  broken  stem?  of  infested 
whcai  had  bent  in  such  a  way  as  to  crush  and  kill  the  larva  which  was 
working  at  the  point  where  the  stem  collapsed.  Since  the  stem-  of 
grasses  do  not  break  under  the  attack,  this  is  a  danger  which  the  in- 
sect has  incurred  by  changing  to  a  new  food  plant.  This  form  of 
accident  materially  reduces  the  number  of  individuals  which  may 
reach  maturity  and  deposit  eggs  in  the  wheat,  since  from  6  to  7.~>  per 
cent  of  the  infested  stems  break  near  the  point  where  the  larva  is 
working,  shortly  before  the  larva  reti'eats  toward  the  roots  to  pre- 
pare for  hibernation. 

Parasites  were  reared  by  the  junior  author  from  larvae  collected  at 
Minot,  X.  Dak.,  belonging  to  an  undescribed  specie-  of  the  Chalcidid 
tribe  Entedonini. 

PREVENTIVE    MEAS1  R]  S. 

Mr.  Criddle  tried  burning  the  stubble  in  the  autumn  with  the  aid 
of  straw  scattered  over  it,  but  found  thai  the  larva'  were  not  much 
damaged  thereby.  A  remedy  which  suggests  itself  and  has  been 
practiced  to  some  extent  is  the  plowing  down  of  all  stubble,  either  in 
autumn  or  before  June  15,  at  which  time  the  adults  may  lie  expected 
to  emerge  and  deposit  eggs.  Grass  growing  near  the  edges  of  fields 
should  be  mowed  early  in  July,  while  the  larvae  are  small,  to  prevenl 
them  from  maturing  and  attacking  the  crop  of  the  following  year. 

Approved : 

James  Wilson. 

St  -  /■'  tary  <>i  .  I  griculturi . 
Washington,  I).  C,  December  24,  1909. 

[Clr.  117] 

o 


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